The present invention relates to a multi-inlet vacuum pump.
Multi-inlet vacuum pumps comprise, in a common housing, a plurality of pump devices provided e.g. as turbomolecular pumps, optionally in connection with a Holweck stage. The individual pump devices are usually carried by a common rotor shaft and driven by a single electric motor. The pump housing comprises a main inlet provided for suctional intake of a first fluid stream by operation of the first pump device. After passing through the first pump device, the first fluid stream will be conveyed in the direction of an outlet by the second pump device and optionally by further pump devices. Between the first and second pump devices, an intermediate inlet is provided for suctional intake of a second fluid stream by operation of the second pump device. The second pump device will thus convey the first and second fluid streams in the direction of the outlet. Optionally, a second intermediate inlet can be provided between the second pump device and a third pump device. By the third pump device, also a corresponding third fluid stream is conveyed in the direction of the outlet, wherein, thereafter, all of said three fluid streams are conveyed by the third pump device.
From EP 0 919 726 (U.S. Pat. No. 6,106,223), a multi-inlet pump is known wherein the outer diameter of the rotor disks of the first pump device is smaller than the outer diameter of the rotor disks of the second pump device. Thereby, a relatively high suction capacity is realized at the intermediate inlet.
It is an object of the invention to provide a multi-inlet vacuum pump which has an improved partial pressure and offers the possibility of an increased suction capacity at the intermediate inlet.